Conventionally, laser microspectroscopes of confocal optical systems that are suitable for a point analysis of a sample is known. This device irradiates a laser light onto a micro region of a sample at pinpoint and forms a beam spot having a diameter size of approximately 1 μm. Then, it obtains spectra of the light from the point with high spatial resolution. Specifically, an objective lens, an imaging lens and a single aperture are used to focus the light from the sample with the objective lens and form its image by the imaging lens, and the opening of the single aperture is positioned at an imaging position. At this point, the light other than the light from the focus of the objective lens is blocked. Therefore, a point analysis with high spatial resolution is possible by spectrally separating the passing light by a spectrometer and detecting spectra by a detector (Patent Literature 1).
Recently, needs for microspectroscopes suitable for performing an area analysis over a wide region of a sample are increasing. A mapping measurement (also referred to as a point mapping) which repeats conventional point analysis for each point of a plurality of measurement points of a sample cannot meet the needs sufficiently from the viewpoint of the measurement time due to excess measurement points. If an exposure time per one point is shortened, S/N of the spectrum will be deteriorated. Therefore, the exposure time cannot be shortened.
From the viewpoint of shortening of the measurement time of the area analysis, several mapping measurement techniques have been proposed. Among them, there is a method which irradiates an irradiation light linearly onto a sample and collectively obtains spectra of a plurality of points from the vertically long irradiation region (referred to as a line mapping). In Patent Literature 2, a line mapping that forms a linear irradiation region on a sample by a method of deflecting a beam spot in the Y direction at high speed is disclosed. The irradiation light is irradiated onto the sample in a spot-shape, and when the beam spot is moved in the Y direction by a deflecting unit such as an acousto-optical element, the spot image moves along a slit in an incident slit of a spectrometer. During an exposure period of a CCD detector, the beam spot is moved in the Y direction once or more times so that the sample is linearly irradiated and a plurality of spectra that correspond to a plurality of measurement points in the linear irradiation area is read out during its read-out period. Consequently, within one frame of the CCD detector, a plurality of spectra in the linear irradiation region is obtained collectively. Once imaging of one frame is finished, the sample is shifted in the X direction to repeat the same line irradiation. Such mapping measurement is referred to as a “conventional line mapping” in this context.
In this context, resolution and detection sensitivity defined as follows are used. Spatial resolution is a measurement capability to distinguish two points that are spatially close to each other. Wavelength resolution (also referred to as spectral resolution) is a measurement capability to distinguish two peaks that are close to each other on the spectrum. Detection sensitivity is a ratio of a quantity of the incident light to the detector to a quantity of the irradiation light to the sample. When the quantities of the irradiation light to the sample are the same, the detection sensitivity is higher for those with larger quantity of the incident light to the detector. That is, sufficient quantity of the incident light to the detector may be obtained although the irradiation time to the sample is short.